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As a pediatrician, I haven't made a big deal about fights between siblings. Because of a study just released, I have decided to make a bigger deal about it.

Brothers and sisters fight--it's pretty universal. I don't think I've ever met a family with more than one kid where the kids didn't fight, sometimes a lot. So over the years, when families have told me about sibling fights, what I've done is a.make sure there wasn't serious physical, verbal or emotional stuff going on, and b.make sure the kids weren't having behavioral problems outside of the home. If neither was happening, while I always encourage intervening, I have generally let it pass.

I shouldn't have done that.

In the study, published in the journal Pediatrics, researchers interviewed more than 3500 children and their families about aggression between siblings. They asked about physical aggression, stealing, breaking things on purpose--and also about saying things to make a sibling feel bad, scared, or not wanted around. They found that even mild aggression had a negative effect on the mental health of the victim.

It makes sense, when you think about it. You can't escape your siblings--they live with you. And when someone who knows you that well, and is supposed to love you, does hurtful things to you --well, that can be more hurtful than when someone outside the family does the same thing.

I'm very happy to change my advice, because as a parent, I'm strict about fights between my kids. I'm not going to say that my kids never fight. Of course they do. But I always react--and I absolutely never tolerate anything physical or anything mean. I insist on kindness, sharing and fairness always.

Now I've got medical research to back me up. It's so cool when that happens.

So the next time your kids start fighting, don't just roll your eyes and think, "kids will be kids." Intervene. Have consequences for bad behavior. Even better, set ground rules. Make it an expectation that everyone in the family be treated well. That means no name-calling, no making fun of people or degrading people, no being rude. It means respecting privacy and property. It means sharing food, stuff and space. It means never being hurtful, either physically or emotionally.

Setting these ground rules is not only important for the mental health of your children, it teaches them an important lesson: everyone in this world is deserving of kindness. Because if you can be unkind to your brother or sister, that means that you don't always have to be kind--even to the people closest to you.

And that, I hope, isn't what you want your child to grow up believing. True kindness, after all, doesn't make exceptions.

Is there something you'd like me to write about? Leave me a message on my Facebook page--and "like" the page for links to all my MD Mama blogs as well as my blogs on Thriving and Huffington Post.

This blog is not written or edited by Boston.com or the Boston Globe.
The author is solely responsible for the content.

About MD Mama

Claire McCarthy, M.D., is a pediatrician and Medical Communications Editor at Boston Children's Hospital . An assistant professor of pediatrics at Harvard Medical School and a senior editor for Harvard
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